Field Project's Cruise 2009 Science: Focus on Diurnal SST and

Sargassum

Christa Blaisdell and Eric AronchickDepartment of Marine and Environmental Systems

Florida Institute of Technology

July 22, 2009

Cruise Activities

Sea Surface Temperature and its Diurnal Cycle

• Influenced by – Wind induced

turbulence– Net radiative

flux

• Needed for numerical weather prediction and climatic research

Average Diurnal Cycle Variation in SST

Time of Day

Tem

pera

ture

(ºC

)

Sunrise ~2pm

Photo Courtesy of GHRSST

Conductivity-Temperature-Depth (CTD) and Sea Temperature

25.5 26 26.5 27 27.5 280

2

4

6

8

10

12

14

16

0130 UTC

0330 UTC

0530 UTC

0730 UTC

Temperature (ºC)

Dep

th (

m)

What’s the Problem?

How do we measure SST from a moving platform?

Moderate Resolution Imaging Spectroradiometer (MODIS)

• Part of NASA’s Global Climate Change Research Program – Earth Observing System

(EOS)• Located aboard EOS Terra and

Aqua satellites

• Data collected using 11 μm channel– Get SST from outgoing IR

emission

SST = 11μmSargassum = 0.6 μm

Retrieving the Diurnal Cycle

• Geospatial issues• Use MODIS as a baseline

– MODIS is frozen in time– Scale out changes

• Poor assumptions = weak diurnal curve

Advection Upwelling

RV Savannah Sea Surface Temperature (ºC) minus MODIS Satellite Sea Surface (ºC) Temperature with Respect to hour of day (UTC) for June 17th to

June 19th, 2009Te

mpe

ratu

re D

iffe

renc

e (º

C)

Hour of Day (UTC)

RV Savannah Sea Surface Temperature (ºC) minus MODIS Satellite Sea Surface (ºC) Temperature with Respect to hour of day (UTC) for June 17th to

June 19th, 2009Te

mpe

ratu

re D

iffe

renc

e (º

C)

Hour of Day (UTC)

Amplitude ≈ 1.8 ºC

Diurnal warming in SST

Peak Solar Insulation (W/m2)

Daily Averaged Precipitation (in)

Daily Averaged 10m Wind (m/s)

Day/Side of Wind Amplitude17th Port Wind 1.6717th Starboard Wind 1.6318th Port Wind 1.9118th Starboard Wind 1.9319th Port Wind 1.4919th Starboard Wind 1.49

Day Average Amplitude

17th 1.65

18th 1.92

19th 1.49

3 Day Average Amplitude = 1.69 ºC

What can we conclude?

• Our method using the empirical formula is reasonable–Most changes due to diurnal changes– Leads to addressing geospatial issues– Fits “standard” model results

What is Sargassum?

• Genus of Brown Macroalgae (seaweed)

• Commonly thought to originate from Sargasso Sea in the Atlantic basin

• Floats on Surface of Water (top 2m)

• May grow to several meters in length/width

• Very diverse community

• provides shelter

• provides food

• provides protection

Satellite Remote Sensing and Sargassum

• What motivates us to do this?– Ability to detect Sargassum from

Space

– Geospatial aspects of Sargassum• Where does it come from?• Where does it go?• Are these widths realistic?

– Convert Sargassum signals to densities• Sargassum tows• How much is there?

• Previous studies– Signatures and patterns

– Spatial validation

– Different Signatures (courtesy of)• FAI (Chuanmin)• MCI (Gower)• FLH (Gower)

MCI Image Sargassum: sargassumfromspace.org/archive.php

60km

300m Full Resolution

MERIS

• Medium Resolution Imaging Spectrometer

• One of the main components on board the European Space Agency’s Envisat Platform

• Operates in the solar radiative spectral range

• Utilizes a 709 micron band

• Essential to detecting Sargassum – Gower

Procedures & Methods

• MODIS & MERIS downloads/data retrieval

• Process and generate images:

• Fluorescent Line Height (FLH)

• Maximum Chlorophyll Index (MCI)

• Floral Algal Index (FAI)

• Chromophoric Dissolved Organic Matter (CDOM)

• Based off Normalized Difference Vegetation Index

(NDVI)

• Inspect figures for Sargassum patterns

• Look for relationships between CDOM and Yellow Substance

• Compare over 100,000 data points/values from R/V Savannah to

downloaded MERIS and MODIS

Procedures & Methods Continued

Floral Algal Index

• Measures NDVI over oceans

• Most common vegetation index for satellite imagery

• Determines whether sample area contains live floating algae 2500km

150km

500-750m wide

Hu, Chaunmin 2008

MERIS MCI

July 18th 2009

12:30 pm

Sargassum Sighting

• Maximum Chlorophyll Index

• Measures the water leaving radiance at a peak of 709nm

• Indicates high surface concentrations of chlorophyll_a

• “Red edge” – 680-750nm

(Gower; et.al. 2008)60km

600 – 900m in width

Fluorescent Line Height

• Relative measure of the amount of radiance leaving the sea surface

• Measured in chlorophyll fluorescence emission band

• 678nm signal

• Result of chlorophyll fluorescence 75km

Oceancolor.gsfc.nasa.gov 2009

What We Saw

• Collected 8kg Sargassum• 1m2 area

• Approximately 0.01kg/m2 Sargassum

• 250m x 250m quadrant• Equals 1% total Sargassum

coverage

Sample Area: 250m x 250m

Floral Algal Index

50km

MERIS MCI

50km

Fluorescent Line Height

•June 18th 2009 12:30 pm

•Sargassum Sighting

•Elevated FLH Levels

•Western Edge of Gulf Stream

50km

CDOM and Yellow Substance

• CDOM created by Sargassum

• Yellow Substance = CDOM

• YS = absorption coefficient (1/m)

• CDOM = density (ppb)

• Elevated levels of Yellow Substance

50km

Summary

• Didn’t see strong signatures of Sargassum

• Didn’t see great in situ concentrations of Sargassum

• For the Future:• Target areas with Sargassum • More extensive surface tows• Flight support option

• Translate between remote sensing and in situ.

Special thanks to:•Professor Michael Splitt for his assistance throughout the 2009 Field Project Summer Cruise research.

•The European Space Agency for providing the MERIS software free of charge

Bostater, Charles. Personal Interview

Sean Baily. Article. Ocean Color WebSite.

WETLabs. CDOM WETStar Characterization. November 13, 2008

www.wikipedia.com

Zepp; et.al. “Photobiochemistry of Sargassum: A Potentially Important Source of Chromophoric Dissolved Organic Matter in the Upper Ocean”. U.S. Environmental Protection Agency

Abbott, Mark; Letelier, Ricardo. “Algorithm Theoretical Basis Document. Chlorophyll Fluorescence (MODIS Product Number 20)”. Oregon State University, College of Oceanic and Atmospheric Sciences

Doerffer; Schiller. “The MERIS Case 2 Water Algorithm”. International Journal of Remote Sensing. vol. 28. no. 3-4. pp. 517-535. 2007

Gower, Jim; King, Stephanie. “New Results from a Global Survey Using MERIS MCI”. Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, BC. V8L 4B2. 2008

Gower, Jim; Hu, Chuanmin; Borstad, Gary; King, Stephanie. “Ocean Color Satellites Show Extensive Lines of Floating Sargassum in the Gulf of Mexico”. IEEE Transactions on Geoscience and Remote Sensing. vol. 44. no. 12. pp. 3619-3625. 2006

Gower, Jim; King, Stephanie. “Sargassum from Space”. Institute of Ocean Sciences Fisheries and Oceans Canada, Sidney, BC, Canada. Presentation

Bernie, D. J., Woolnough, S. J., Slingo, J. M., & Guilyardi, E. Modeling Diurnal and Intraseasonal Variability of the Ocean Mixed Layer. Journal of Climate , 18, 1190-1202.

Clayson, C. A., & Weitlich, D. Variability of Tropical Diurnal Sea Surface Temperature. Journal of Climate , 20, 334-352.

Gentemann, C. L., Donlon, C. J., Stuart-Menteth, A., & Wentz, F. J. (2003). Diurnal signals in satellite sea surface temperature measurements. Geophysical Research Letters , 30 (3), 1140.

National Aeronautics and Space Administration. (n.d.). MODIS Web. Retrieved from NASA: http://modis.gsfc.nasa.gov/

What is Diurnal Variability? (n.d.). Retrieved from Group for High Resolution Sea Surface Temperature: http://www.ghrsst-pp.org/What-is-diurnal-variability.html

REFERENCES

Questions?